1. Field of the Invention
The present invention relates to an optical disk apparatus for recording and reproducing information on an optical disk.
2. Related Background Art
In recent years, optical disks have become the mainstream for information recording media with large storage capacity, as used for example for data of multi-media applications. In order to increase their capacity even further, optical disks with high density storage capability (referred to in short as xe2x80x9chigh-density disksxe2x80x9d in the following) are being proposed continuously.
The main strategies in achieving higher densities are making the recording marks shorter and making the track pitch narrower. However, as the densities increase, changes in the focusing condition of the light beam due to defocusing or tilting of the disk during recording or reproduction exert a greater influence on the signal quality, such as the S/N ratio for example. Therefore, it is preferable to record at a laser power in which the decrease of the equivalent laser power due to the change in the focusing condition is compensated.
With regard to this problem, a method has been proposed, that detects the minimum recording power for forming reproducible recording marks (that is, at the reproducible limit) on the optical disk (referred to as xe2x80x9cminimum recording powerxe2x80x9d or xe2x80x9cPminxe2x80x9d in the following), and that sets the laser power used for recording data to an optimum recording power obtained by multiplying this Pmin by a certain factor (see for example, JP H03-232141A).
The following is an explanation of an example of such a conventional optical disk apparatus, with reference to the accompanying drawings.
FIG. 18 is a block diagram illustrating the configuration of a conventional optical disk apparatus. In FIG. 18, numeral 1 denotes an optical disk, numeral 2 denotes a spindle motor for rotating the optical disk 1, and numeral 3 denotes an optical head focusing laser light on the optical disk 1 and detecting recorded information from the light reflected by the optical disk 1. Numeral 4 denotes a laser power control portion, which sets the laser power depending on information input from a control portion 9 explained below, and numeral 5 denotes a magnetic head for the recording of signals. Numeral 6 denotes a band-pass filter (BPF), and numeral 7 denotes a detector for detecting the strength of the reproduction signal. Numeral 8 denotes a minimum recording power detection portion for detecting Pmin. Numeral 9 is a control portion, which controls the spindle motor 2, the optical head. 3, the laser power control portion 4, and the magnetic head 5 and sets the optimum recording power.
The following is an explanation of the operation of an optical disk apparatus with the above configuration.
To set the laser power used for the recording of data, first, the laser power control portion 4 sets the power based on information from the control portion 9. The control portion 9 controls the optical head 3 and the magnetic head 5, and lets them record a single-frequency signal on the optical disk 1. Then, this signal is reproduced with the optical head 3, and after band limiting with the band-pass filter 6, which has a pass band including the recorded frequency, the signal strength of the output signal is detected with the detector 7 and input into the minimum recording power detection portion 8.
Repeating this operation while changing the value to which the recording power is set leads to a dependency of the reproduction signal intensity on the recording power as shown in FIG. 19. The minimum recording power detection portion 8 detects Pmin by approximate calculation from the recording power dependency shown in FIG. 19. The detected Pmin is input into the control portion 9. Multiplying Pmin by a factor and taking the resulting value as the optimum recording power, the control portion 9 sets the laser power used for the recording of data, thus making it possible to preserve constant recording conditions, even when the focusing of the light beam or the temperature of the optical disk change.
However, in this configuration, Pmin is detected using the signal strength of the reproduction signal, so that Pmin has to be detected in regions in which no data has yet been recorded. Therefore, the detection of Pmin has to be performed in a predetermined region provided on the optical disk as a power setting region for example, or, if the detection of Pmin is performed in the data recording region, then the data recorded in that region have to be deleted beforehand. In the former case, the space on the optical disk that cannot be used for the recording of data increases, so that the data recording capacity decreases, whereas the latter case causes a rotational delay for deleting the data and the detection of Pmin takes extra time, and furthermore, there is the risk that during the deletion, the data on neighboring tracks are deleted as well (cross-erasing).
It is an object of the present invention to provide an optical disk apparatus, wherein, when taking a data recording region as the region for detecting the minimum recording power, it is not necessary to delete beforehand data that are recorded in that region, and in which Pmin can be detected with high precision and in a short time.
In order to attain this object, in accordance with the present invention, a first optical disk apparatus for recording and reproducing data by irradiating a light beam onto an optical disk includes a recording portion for recording information on the optical disk; a laser power control portion for controlling a laser power of the recording portion; a reproduction portion for reproducing information recorded on the optical disk; a correlation detection portion for detecting a correlation between a recording pattern to be recorded on the optical disk by the recording portion and a reproduction signal obtained when the recording pattern is reproduced by the reproduction portion; and an optimum recording power setting portion which detects a minimum recording power at which reproducible recording marks are formed on the optical disk, and sets an optimum recording power to a power obtained by multiplying this minimum recording power by a recording compensating factor; wherein the optimum recording power setting portion compares a predetermined level with an output by the correlation detection portion that is obtained when the laser power is changed stepwise by the laser power control portion, detects as the minimum recording power the recording power when the originally smaller of the predetermined level and that output by the correlation detection portion becomes larger than the other, and sets the optimum recording power.
In this first optical disk apparatus, it is preferable that the optimum recording power setting portion detects the minimum recording power in a plurality of regions on the optical disk, and sets a common optimum recording power for this plurality of regions.
In this first optical disk apparatus, it is also preferable that the recording of data is interrupted if the optimum recording power setting portion determines, based on the detected minimum recording power, that no suitable optimum recording power exists.
In this first optical disk apparatus, it is also preferable that the recording portion records a recording pattern in which the frequency of xe2x80x9c0xe2x80x9ds and xe2x80x9c1xe2x80x9ds when detecting the minimum recording power is substantially equal.
In this first optical disk apparatus, it is also preferable that the recording portion records a different recording pattern each time the minimum recording power is detected.
In order to attain the above-mentioned object, in accordance with the present invention, a second optical disk apparatus for recording and reproducing data by irradiating a light beam onto an optical disk includes a recording portion for recording information on the optical disk; a laser power control portion for controlling a laser power of the recording portion; a reproduction portion for reproducing information recorded on the optical disk; a correlation detection portion for detecting a correlation between a recording pattern to be recorded on the optical disk by the recording portion and a reproduction signal obtained when the recording pattern is reproduced by the reproduction portion; an optimum recording power setting portion which detects a minimum recording power at which reproducible recording marks are formed on the optical disk, and sets an optimum recording power to a power obtained by multiplying this minimum recording power by a recording compensating factor; and a position specification portion for specifying a position on the optical disk where the minimum recording power is detected; wherein the optimum recording power setting portion compares a predetermined level with an output by the correlation detection portion that is obtained when the laser power at the position specified by the position specification portion is changed stepwise by the laser power control portion, detects as the minimum recording power the recording power when the originally smaller of the predetermined level and that output by the correlation detection portion becomes larger than the other, and sets the optimum recording power.
In this second optical disk apparatus, it is preferable that the position specification portion specifies a data recording region.
In order to attain above-mentioned object, in accordance with the present invention, a third optical disk apparatus for recording and reproducing data by irradiating a light beam onto an optical disk having a power setting region provided separately from a data recording region, the optical disk apparatus includes a recording portion for recording information on the optical disk; a laser power control portion for controlling a laser power of the recording portion; a reproduction portion for reproducing information recorded on the optical disk; a correlation detection portion for detecting a correlation between a recording pattern to be recorded on the optical disk by the recording portion and a reproduction signal obtained when the recording pattern is reproduced by the reproduction portion; an optimum recording power setting portion which detects a minimum recording power at which reproducible recording marks are formed on the optical disk, and sets an optimum recording power to a power obtained by multiplying this minimum recording power by a recording compensating factor; a position specification portion for specifying a position on the optical disk where the minimum recording power is detected; and a detection power specification portion, which specifies a maximum laser power used for detecting the minimum recording power; wherein the position specification portion specifies the power setting region before the data recording region, and the optimum recording power setting portion compares a predetermined level with an output by the correlation detection portion that is obtained when the laser power at the position specified by the position specification portion is changed stepwise by the laser power control portion, detects as the minimum recording power the recording power when the originally smaller of the predetermined level and that output by the correlation detection portion becomes larger than the other, sets the optimum recording power to that recording power, inputs the detected minimum recording power into the detection power specification portion, and determines the maximum laser power.
In order to attain above-mentioned object, in accordance with the present invention, a fourth optical disk apparatus for recording and reproducing data by irradiating a light beam onto an optical disk includes a recording portion for recording information on the optical disk; a laser power control portion for controlling a laser power of the recording portion; a reproduction portion for reproducing information recorded on the optical disk; a correlation detection portion for detecting a correlation between a recording pattern to be recorded on the optical disk by the recording portion and a reproduction signal obtained when the recording pattern is reproduced by the reproduction portion; an optimum recording power setting portion which detects a minimum recording power at which reproducible recording marks are formed on the optical disk, and sets an optimum recording power to a power obtained by multiplying this minimum recording power by a recording compensating factor; and a timing specification portion specifying a timing for detecting the minimum recording power; wherein the optimum recording power setting portion compares a predetermined level with an output by the correlation detection portion that is obtained when the laser power is changed stepwise by the laser power control portion at the timing specified by the timing specification portion, detects as the minimum recording power the recording power when the originally smaller of the predetermined level and that output by the correlation detection portion becomes larger than the other, and sets the optimum recording power.
In this fourth optical disk apparatus, it is preferable that a temperature change near the optical disk is detected and the timing specification portion specifies a time when that temperature change has reached a predetermined value as the timing for detecting the minimum recording power.
In this fourth optical disk apparatus, it is also preferable that the timing specification portion specifies a time when a predetermined time has passed after detecting the minimum recording power as the timing for detecting the minimum recording power.
With the above-described configurations, when taking a data recording region as the region for detecting the minimum recording power, it is not necessary to delete beforehand data that are recorded in that region, and Pmin can be detected with high precision and in a short time.
Furthermore, it is possible to detect Pmin at positions (sectors) immediately prior to recording, so that even in the case of tilting or warping of the optical disk, or temporal changes such as defocusing or temperature changes, it is still possible to set an optimum recording power.
Furthermore, by detecting Pmin in a power setting region, and specifying a maximum laser power used for the detection of Pmin based on that value, it is possible to prevent cross-writing in high-density disks.
Furthermore, when the temperature changes abruptly, then this is detected, Pmin is detected again, and the recording power used for the recording of data is set again, so that it is still possible to set an optimum recording power.
It is preferable that the above-described first to fourth optical disk apparatuses further include a factor setting portion for setting the value of said recording compensating factor.
Furthermore, it is preferable that the factor setting portion sets the value of said recording compensating factor in accordance with a temperature of the optical disk.
It is also preferable that the factor setting portion sets the value of said recording compensating factor in accordance with a linear speed of the optical disk.
It is also preferable that the factor setting portion sets the value of said recording compensating factor in accordance with a focusing condition of the light beam. In that case, the focusing condition of the light beam can be determined from the minimum recording power at which reproducible recording marks are formed.
If the optical disk apparatus records data by irradiating the light beam intermittently, then it is preferable that the factor setting portion sets the value of said recording compensating factor in accordance with an intermittency ratio of the light beam.
With the above-described configuration, it becomes possible to set the recording compensating factor by which the minimum recording power is multiplied when setting the laser power used for the recording of data (optimum recording power) to an optimum value in accordance with, for example, the focusing condition of the light beam at the time of recording.
Furthermore, if the light beam is irradiated intermittently during the recording, it is possible to set the recording compensating factor by which the minimum recording power is multiplied to an optimum value in accordance with the intermittency ratio.
These and other objects, features and advantageous effects of the present invention will become apparent from the following description, with reference to the accompanying drawings.